Combinations of levodopa (LD) and a decarboxylase inhibitor (typically carbidopa (CD)) to treat Parkinson's disease (PD) are known in the pharmaceutical arts and are considered by many to be the ‘gold standard’ treatment for symptoms of PD. Currently, several formulations containing a combination of LD and CD are commercially available, e.g., SINEMET®, STALEVO®, PARCOPA®, and ATAMET®. Nonetheless, a need remains for an oral LD formulation that provides steadier plasma concentrations of LD with minimal ‘peak-to-trough’ fluctuations during daily dosing and that yields a longer duration-of-effect than the currently available oral dosage forms of CD/LD.
Patients suffering from PD frequently have periods in which their mobility becomes difficult, often resulting in an inability to move. Abnormally low levels of dopamine, a neurotransmitter that affects mobility and control of the skeletal-muscular system, is commonly believed to be the cause of these motor symptoms in PD patients. However, administration of dopamine is not effective to treat Parkinson's disease because dopamine does not cross the blood-brain barrier. To resolve this problem, PD patients are administered levodopa, the metabolic precursor of dopamine, but levodopa is not without its issues either.
While levodopa crosses the blood-brain barrier and is rapidly converted to dopamine, LD is problematic because of its rapid decarboxylation by tissues other than the brain. Thus, when LD is administered alone, large doses are required because only a small portion is transported to the brain unchanged. Furthermore, when levodopa is administered orally it is rapidly decarboxylated to dopamine in extracerebral tissues so that only a small portion of a given dose is transported unchanged to the central nervous system. Carbidopa inhibits the decarboxylation of peripheral levodopa and does not cross the blood-brain barrier. Since its decarboxylase inhibiting activity is limited to extracerebral tissues, administration of carbidopa with levodopa has been popular to make levodopa more available for transport to the brain.
In addition to these difficulties associated with absorption of LD, over time patients treated with LD also exhibit symptoms of “wearing off”. PD patients treated with LD may develop motor fluctuations characterized by end-of-dose failure, peak dose dyskinesia, and akinesia. The advanced form of motor fluctuations (also commonly referred to as the ‘on-off’ phenomenon) is characterized by unpredictable swings from mobility to immobility. Although the causes of these motor fluctuations are not completely understood, some patients may be attenuated by treatment regimens that produce steady plasma levels of LD. Thus, a void remains in the LD treatment of PD patients, as plasma concentration levels remain difficult to control.
Currently available controlled release formulations of CD/LD are meant to allow for a continuous release of drug over a prolonged period of time in an attempt to maintain tight LD plasma ranges. However, the use of these controlled release dosage forms are problematic in that many PD patients wake up in the morning having little or no mobility due to the wearing of the dose taken the day/evening before. Once the previous dose has worn off, such patients are usually unwilling, or even unable, to wait for the extended period of time required for a controlled release dosage form to deliver the necessary plasma levels of LD. While the use of an immediate release formulation of LD can reduce this ‘wait time’, the use of an immediate release formulation of LD require more frequent dosing and are associated with more fluctuating plasma LD concentrations. DUODOPA®, an intraduodenal infusion therapy approved outside of the United States, demonstrates significantly reduced motor complications and reduced ‘off’ time. The cumulative experiences from DUODOPA® and experimental infusion studies show that the maintenance of stable plasma LD concentrations and the avoidance of low trough levels appear to be effective in reducing ‘off’ time, increasing ‘on’ time without disabling dyskinesia, and reduce the severity of dyskinesia in comparison to the standard oral formulations. However, such infusion therapies are extremely inconvenient to the patient.
The results of infusion therapies, such as DUODOPA®, strongly suggest a rationale for the development of a LD treatment that provide constant, or relatively steady, LD plasma concentrations to optimize relief of PD symptoms and to minimize ‘off’ times and dyskinesias. Indeed, a need remains for a more convenient, i.e., oral, dosage form that will improve the administration of LD to PD patients by narrowing blood plasma ranges of LD, which in turn will result in reduced ‘off times’, prolonged ‘on time’, and decreased time to ‘on’. The present invention fills this void by providing a novel controlled release oral solid dosage form of LD that is formulated with a decarboxylase inhibitor and an acid, to yield the desired pharmacokinetic attributes, i.e., steadier plasma concentrations of LD over a prolonged period of time.